Device for automatically stopping delivery of liquid by a centrifugal pump during reverse operation thereof

ABSTRACT

Device for automatically stopping delivery of liquid by a centrifugal pump operating in reverse running condition through the introduction of air into the pump chamber of the pump includes means defining a bore formed in the housing of the pump for connecting the pump chamber to atmosphere, and means cooperating with the bore-defining means for adjusting the pressure in the pump chamber to positive pressure in forward running condition of the pump rotor and to negative pressure in reverse running condition thereof whereby in the latter condition air is sucked from the atmosphere into the pump chamber to stop delivery of liquid by the pump.

United States Patent Schiinwald [54] DEVICE FOR AUTOMATICALLY STOPPINGDELIVERY OF LIQUID BY A CENTRIFUGAL PUMP DURING REVERSE OPERATIONTHEREOF [72] Inventor: Siegfried Schiinwald, Bad Neustadt, Saale,

Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin, Germany [22]Filed: July 14,1969

[21] App1.No.: 841,299

[451 May 2,1972

Primary Examiner-Henry F. Raduazo Attorney-Curt M. Avery, Arthur E.Wilfond, Herbert L. Lerner and Daniel J. Tick 5 7] ABSTRACT Device forautomatically stopping delivery of liquid by a centrifugal pumpoperating in reverse running condition through the introduction of airinto the pump chamber of the pump includes means defining a bore formedin the housing of the pump for connecting the pump chamber toatmosphere, and means cooperating with the bore-defining means foradjusting the pressure in the pump chamber to positive pressure inforward running condition of the pump rotor and to negative pressure inreverse running condition thereof whereby in the latter condition air issucked from the atmosphere into the pump chamber to stop delivery ofliquid by the pump.

12 Claims, 6 Drawing Figures DEVICE FOR AUTOMATICALLY STOPPING DELIVERYOF LIQUID BY A CENTRIFUGAL PUMP DURING REVERSE OPERATION THEREOF Myinvention relates to device for automatically stopping delivery ofliquid by a radial centrifugal pump having a spiral housing, duringreverse operation of the pump, by introducing air into the pump chamber.

A centrifugal pump of radial construction delivers liquid, duringreverse rotation of the pump rotor, in the same flowthrough direction asduring nonnal or forward rotation of the pump rotor, although withmarkedly reduced pumping power. This delivery of liquid during reverseoperation of the pump must be stopped if, for example, a second pumpassembly operates from the same drive shaft as the first-mentioned pumpand is dependent on rotary direction, as is, for example, the case withcirculating and draining or discharge pumps of dishwashing machines, Afurther requirement is that the delivery of liquid should stop from thevery instant that the pump is switched from forward to reverse operationso that as little liquid as possible leaves the pump at the pressureside thereof.

The delivery of a centrifugal pump having suction tubes to which liquid,such as, water, runs, can be stopped by partly filling the rotor chamberthereof with air. Since the liquid, such as water, present in the pumpchamber forms a circulating ring due to centrifugal action, the airtends to keep to the inner rotor space. Consequently, only a relativelysmall pressure increase is possible from the rotor inner diameter to therotor outer diameter; the liquid (water) flowing to the suction tubescannot penetrate into the rotor chamber.

This operating condition of the pump is known as snapping-off." Theproblem that is thus presented is to bring the pump to a rapidsnapping-off" condition during reverse operation thereof even when thesuction tube is full, yet not prevent this effect from occuring when thepump is in forward operation,

ln this regard, it has become known to insert into the liquid flow adynamic pressure or backpressure tube which is connected to the outerair. During reverse rotation of the pump rotor, air is sucked from theoutside into the pump housing through this tube by a sort of jet pumpaction, and the delivery of liquid is thereby stopped; during forwardrotation of the rotor, the liquid accumulates at the tube so that asmall portion thereof can leave the pump chamber. Such an arrangement isdisadvantageous however, inasmuch as the liquid flow is disturbed by thedynamic pressure tube under certain conditions during forward rotationof the pump rotor; and because there is constant danger of obstructionof the quite narrow dynamic pressure tube by dirt which is present inthe liquid i.e., water, as for example in the case of circulating pumps.Furthermore, due consideration must be given to the fact that thedynamic pressure tube is relatively costly.

lt is accordingly an object of my invention to provide device forautomatically stopping delivery of liquid by a centrifugal pump duringreverse operation of the latter which avoids the disadvantages of theheretofore known devices for effecting this purpose. More specifically,objects of my invention are to provide such device which will notdisturb liquid flow during forward rotation of the pump rotor, whichwill not present any danger of obstruction, and which will moreover berelatively inexpensive.

With the foregoing and other objects in view, I provide, according to myinvention, device for automatically stopping delivery of liquid by acentrifugal pump during reverse operation thereof by introducing airinto the pump chamber of the pump, comprising means defining a boreformed in the housing of the pump for connecting the pump chamber of thepump to atmosphere, and means cooperating with the boredefining meansfor adjusting the pressure in the pump chamber to positive pressure inforward running condition of the pump rotor and to negative pressure inreverse running condition thereof, whereby in the latter condition airis sucked from the atmosphere into the pump chamber to stop delivery ofliquid.

In accordance with another feature of my invention, the bore is formedin a surface of the pump housing that is sub jected to flow dependentupon rotational direction, and a bulge is provided upstream of the borein the reverse rotating direction of the pump rotor. In the forwardrunning condition of the rotor, the liquid flow adjacent the surface ofthe pump housing is blocked by and accumulates at the bulge so that apositive pressure is produced at the bore opening in the pump chamber.In the reverse running condition of the rotor, the liquid flow adjacentthe surface of the pump housing is accelerated as it flows over thebulge so that a negative pressure is produced at the bore opening in thepump chamber.

In accordance with a further feature of the invention, the bulge extendspartly around the bore.

At locations at which a bulge projecu'ng out of the housing wall wouldhave a disturbing efiect, such as for example in the space between thehousing wall and the pump rotor, the flow device comprising the bulgeand the bore-defining means are recessed in the housing wall. Thus, twopockets are machined or otherwise formed in the housing wall, a bulgebeing left between the pockets. The bore is located at an end of one ofthe pockets adjacent the flow-engaging surface of the bulge, which has asteep construction, The surface of the bulge facing away from the boreslopes upwardly from the other pocket. The side surfaces of the pockets,in accordance with another feature of the invention, have an upwardlyopening funnel shape so as to be able to capture as much liquid aspossible.

In accordance with additional features of my invention, thebore-defining means extend transversely to the rotational plane of thepump rotor and are located within the confines of an angle locatedbetween the minimum of the local meridian velocity as the leadinglimiting edge thereof in the rotational sense of the rotor in thereverse running condition thereof and the maximum of the local meridianvelocity as the trailing limiting edge thereof. In other words, the boreis located in a region of the space occupied by the rotor wherein, inthe reverse running condition of the centrifugal pump, the lowestpressure from the inner to the outer diameter of the rotor occurs. Thisregion is characterized by a minimum of the local meridian velocity as aforward or leading limit in the rotational direction of the rotor in thereverse running condition thereof and a maximum of the local meridianvelocity as a rear or trailing limit. This region correspondssubstantially to the confines of the angle respectively 15 forward of to35 behind the tongue point or the narrowest cross section between thehousing wall and the rotor or the location of the smallest angle betweenthe housing wall and the radius vector to the housing wall.

A centrifugal pump of radial construction with a rotor and spiralhousing is conventionallydesigned so that above the rotor space,relative to the rotor, a symmetrical source or intake flow of liquidoccurs i.e., the flow velocities or accelerations in concentric orcoaxial circles in the rotor space are constant. In reverse runningcondition of the pump, the flow pattern over the rotor assumes acompletely different, nonsymmetrical shape due to superimposition of twoflow fields, Also, in reverse rotating condition of the rotor, there ispresent a source or intake flow symmetrical to the rotor yet having areduced source magnitude. This flow is superimposed by a second velocityfield oscillating relative to the rotor due to the guidance of liquid inthe spiral housing. This superimposed velocity, however, in the endregion of the narrowing spiral and as a result of the mass moment ofinertion is directed inwardly a short distance after the tongue pointand outwardly in the remaining part thereof. The meridian velocity ofthe entire flow is accordingly a minimum for example, in the immediatevicinity of the tongue. The meridian velocity increases to a maximumbehind the tongue in the vicinity of the pressure tube extension anduntil entering the spiral. In this region of radially outwardly directedacceleration, the pressure gradient is a minimum i.e., the pressure atfarther radially outward locations of the housing is only slightlygreater or even lower than in the suction opening of the pump. If, forexample, the bore were provided at that location, negative pressurewould occur in the reverse running condition of the pump and air wouldbe sucked into the pump chamber so that the pump would then snapoff. Inforward running condition of the pump, by contrast, the normal positivepressure corresponding to the centrifugal field prevails at this bore sothat liquid is delivered through this bore and no air at all isaspirated.

The pressure reduction adjusted between the minimum and the maximum ofthe meridian velocity for reverse rotational direction of the rotor canbe increased if the intermediate region is shortened in the rotationaldirection, and a greater radial acceleration is thereby produced. Inthis regard, according to my invention, the narrowing spiral is sharplyinwardly bent at the tongue. The minimum of the meridian velocity isthereby lowered more deeply and is displaced toward the pressure tubeextension. To intensify the pressure increase or decrease, the bore inthe pump housing is additionally surrounded by flow guides open to themain liquid flow, in accordance with another feature of my invention.Thus, for example, the bore in the housing wall is provided with theaforementioned bulge at one side thereof which, in another embodiment ofthe invention, partly surrounds the bore so as to increase the blockingof the liquid and thereby the positive pressure at the bore in theforward running condition of the pump.

The aforedescribed flow device including the bore-defining means foradmitting air to the pump chamber is not limited only to theaforedescribed region of alternating pressure but rather can actually beapplied to all surfaces of the pump housing subjected to flow dependentupon rotational direction. Especially advantageous is, of course, theeffect at a location at which the pressure, in the reverse runningcondition of the pump, is in any case already lower than in the forwardrunning condition of the pump. Such a region is found, asaforementioned, transversely to the plane of rotation of the rotor invicinity of the pressure tube extension at the spiral.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin device for automatically stopping delivery of liquid by a centrifugalpump during reverse operation thereof, it is nevertheless not intendedto be limited to the details shown, since various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings, in which:

FIG. 1 is a partly diagrammatic plan view of the pump of my inventionwith the housing cover thereof removed;

FIG. 2 is a plan view of the housing cover removed from the housing ofFIG. 1;

FIGS. 3a and 3b are a top plan view and a longitudinal sectional view,respectively, of one embodiment of the flow guiding device of myinvention wherein the bulge and bore thereof are recessed in the housingwall of the pump; and

FIGS. 4a and 4b are a top plan view and a longitudinal sectional view,respectively of another embodiment of FIGS. 3a and 3b wherein the bulgeprojects from the housing wall of the pump.

Referring now to the drawings and first particularly to FIGS. 1 and 2thereof, there is shown a centrifugal pump having a rotor l which, inforward rotating condition thereof, rotates in the direction of thearrow 20, and liquid, such as water, is flung centrifugally outwardlyfrom the suction opening 3 into the channel 4 widening outwardlyspirally between the rotor l and the housing wall 13, and is dischargedfrom the pump through the pressure tubes 5.

Even in the reverse running condition of the rotor l in direction of thearrow 2b, liquid continues to be delivered although in much-reducedquantity. In order to stop this delivery of liquid, a bore 7 is formedin the pump housing cover 6, and can be connected by a tube to the innerchamber of a dishwashing machine, for example.

The optimum location of the bore is dependent in a known manner upon theconstruction of the pump. lts exact position is variable for example, inaccordance with the amount of bend in the point of the tongue 8 formingpart of the pump housing.

In FIG. 1 there is shown in single-line hatching a region 9 of the pumpsubstantially wherein a bore will produce the desired effect for acentrifugal pump of the illustrated type. This region 9 is radiallyinwardly limited by the fact that negative pressure prevails at thisinner limit both in the forward as well as the reverse operatingconditions of the rotor 1, while the region 9 is limited radiallyoutwardly by the fact that no adequate pressure reduction is realizedany longer at this outer limit in the reverse operating condition of therotor.

If the radius between the rotor axis and the hook-shaped inwardly bentpoint of the tongue 8 is taken as a reference line, the bore 7, in thestructure of the embodiment shown in FIG. 1, is located on a radiusangularly displaced 25 from the reference radius in the reverse runningdirection of the rotor l, and actually still within the confines of thespace occupied by the rotor 1.

To increase the positive pressure and to reduce the negative pressure atthe bore 7, additional flow guides are provided as shown in FIGS. 30, 3band 4a, 4b.

In FIGS. 3a and 3b there is shown one embodiment of the flow guideaccording to my invention wherein two pockets [0 and 11 are machined orotherwise formed in the inner surface of the cover 6 of the pumphousing, a bulge 12 being left between the two pockets. A bore 7 islocated at one end of the pocket 11 adjacent the flow-engaging surfaceof the bulge 12, which has a steep construction. The surface of thebulge 12 facing away from the bore 7 extends upwardly at an inclinationfrom the other pocket 10. The side surfaces of the pockets 10 and 11 arefunnel-shaped and open upwardly as viewed in FIG. 3b so as to capture asmuch of the liquid in the pump, as possible. As seen in FIG. 3b, boththe bulge l2 and the bore 12 are thus recessed in the housing cover 6.

Under certain conditions, the aforedescribed flow device can bedispensed with, in fact when the bore is formed in a recess which hasinclined side surfaces in the reverse running direction of the rotor.The bore and the non-illustrated tube connected thereto are therebyprevented from filiing with spray water in the reverse running conditionof the pump.

In the embodiment of the flow device shown in FIGS. 40 and 4b there isprovided a bore 7 formed in the housing cover 6. In front of the bore 7,as viewed in the forward running condition of the rotor represented bythe arrow 30 there is provided a bulge 22 which partly surrounds thebore 7. In the forward running direction shown by the arrow 30, theliquid flow adjacent the surface of the housing wall and coveraccumulates at the bulge 22 so that a positive pressure is produced atthe bore 7. Consequently, in the forward running direction of the rotor,only water is delivered but no air is aspirated into the pump. In thereverse running condition of the rotor represented by the arrow 3b, theliquid flow adjacent the housing wall and cover is accelerated as itflows over the bulge 22 so that a negative pressure is produced at thebore 1 through which air is sucked into the pump from the outeratmosphere. The pump accordingly snaps off" and the delivery isimmediately and abruptly interrupted.

It must again be emphasized that for the aforedescribed pump, theregions at which the bore may be located approximately coincide. Bysuitable selection of the shape of the pump housing, it is possiblehowever to spread out these regions i.e., to locate the bore at nearlyany desired position of the periphery thereof, for example at a locationat which the radius vector r forms the smallest angle a with the tangentto the wall of the housing, as shown in FIG. 1, or where the channel 4is at its narrowest.

I claim:

1. Device for automatically stopping delivery of liquid by a centrifugalpump having a spiral housing provided with a transverse side wall and arotor with an open blading rotatably mounted therein and operating inreverse running condition through the introduction of air into the pumpchamber of the pump comprising a tongue formed on the spiral housing andprojecting adjacent the periphery of the rotor, means defining a boreformed in the side wall of the housing of the pump for connecting thepump to atmosphere, said means having an abrupt projecting surfaceengageable by the liquid in forward running condition of the pump and asmooth inclined surface, located opposite said abrupt projectingsurface, and engageable by the liquid in reverse running condition ofthe pump, said bore extending transversely to the rotational plane ofthe pump rotor and communicating with the open blading of said pumprotor, said bore being located within the peripheral area covered by therotor blading and said location being within the confines of an angleforward of to 35 behind said tongue in the forward running condition ofthe pump.

2. Device according to claim 1 including means cooperating with saidbore-defining means for adjusting the pressure in the pump chamber topositive pressure in forward running condition of the pump rotor and tonegative pressure in reverse running condition thereof whereby in thelatter condition air is sucked from the atmosphere into the pump chamberto stop delivery of liquid by the pump.

3. Device according to claim 2 wherein said pressure adjusting meanscomprises a bulge located in fluid flow stream of the pump upstream ofsaid bore in the reverse running condition of the pump.

4. Device according to claim 3 wherein said bulge partly surrounds saidbore.

5. Device according to claim 3 wherein two pockets are fonned in thesurface of the pump housing, located between said pockets.

6. Device according to claim 5, wherein said bore is recessed in one ofsaid pockets adjacent said bulge, the side of said bulge facing saidbore having a steep liquid-engaging surface, and the side of said bulgefacing away from said bore extending outwardly at an inclination fromthe other of said pockets.

7. Device according to claim 6 wherein said pockets have side wallsopening outwardly in the shape of a funnel.

8. Device according to claim 7 wherein said bore is located in a recessformed in the side wall of the pump housing, said recess having inclinedwall surfaces extending in the reverse running direction of the pumprotor.

9. Device according to claim 1 wherein the spiral pump housing is formedwith a tongue disposed adjacent the periphery of the pump rotor, saidbore being located on a radius of the rotor displaced substantiallythrough an angle of 25 from a radius of the rotor passing through thetip of said tongue as viewed in reverse running direction of the rotor.

10. Device according to claim 9 wherein the spiral housing has aconstruction wherein an angle a between a tangent to the spiral of thehousing and a radius r located at the vicinity of said tongue is smallerthan at the remaining periphery of said spiral.

11. Device according to claim 9 wherein the tip of said tongue has ahook-like radially inward bend.

12. Device according to claim 1 wherein the bore formed in said pumphousing is surrounded by flow guide means open in direction towardoncoming main liquid flow, said flow guide means, in forward runningcondition of said rotor, being adapted to produce positive pressure atsaid bore and, in reverse running condition of said rotor, to producenegative pressure at said bore.

said bulge being i t i k lOlDJl 056i

1. Device for automatically stopping delivery of liquid by a centrifugalpump having a spiral housing provided with a transverse side wall and arotor with an open blading rotatably mounted therein and operating inreverse running condition through the introduction of air into the pumpchamber of the pump comprising a tongue formed on the spiral housing andprojecting adjacent the periphery of the rotor, means defining a boreformed in the side wall of the housing of the pump for connecting thepump to atmosphere, said means having an abrupt projecting surfaceengageable by the liquid in forward running condition of the pump and asmooth inclined surface, located opposite said abrupt projectingsurface, and engageable by the liquid in reverse running condition ofthe pump, said bore extending transversely to the rotational plane ofthe pump rotor and communicating with the open blading of said pumprotor, said bore being located within the peripheral area covered by therotor blading and said location being within the confines of an angle15* forward of to 35* behind said tongue in the forward runningcondition of the pump.
 2. Device according to claim 1 including meanscooperating with said bore-defining means for adjusting the pressure inthe pump chamber to positive pressure in forwArd running condition ofthe pump rotor and to negative pressure in reverse running conditionthereof whereby in the latter condition air is sucked from theatmosphere into the pump chamber to stop delivery of liquid by the pump.3. Device according to claim 2 wherein said pressure adjusting meanscomprises a bulge located in fluid flow stream of the pump upstream ofsaid bore in the reverse running condition of the pump.
 4. Deviceaccording to claim 3 wherein said bulge partly surrounds said bore. 5.Device according to claim 3 wherein two pockets are formed in thesurface of the pump housing, said bulge being located between saidpockets.
 6. Device according to claim 5, wherein said bore is recessedin one of said pockets adjacent said bulge, the side of said bulgefacing said bore having a steep liquid-engaging surface, and the side ofsaid bulge facing away from said bore extending outwardly at aninclination from the other of said pockets.
 7. Device according to claim6 wherein said pockets have side walls opening outwardly in the shape ofa funnel.
 8. Device according to claim 7 wherein said bore is located ina recess formed in the side wall of the pump housing, said recess havinginclined wall surfaces extending in the reverse running direction of thepump rotor.
 9. Device according to claim 1 wherein the spiral pumphousing is formed with a tongue disposed adjacent the periphery of thepump rotor, said bore being located on a radius of the rotor displacedsubstantially through an angle of 25* from a radius of the rotor passingthrough the tip of said tongue as viewed in reverse running direction ofthe rotor.
 10. Device according to claim 9 wherein the spiral housinghas a construction wherein an angle Alpha between a tangent to thespiral of the housing and a radius r located at the vicinity of saidtongue is smaller than at the remaining periphery of said spiral. 11.Device according to claim 9 wherein the tip of said tongue has ahook-like radially inward bend.
 12. Device according to claim 1 whereinthe bore formed in said pump housing is surrounded by flow guide meansopen in direction toward oncoming main liquid flow, said flow guidemeans, in forward running condition of said rotor, being adapted toproduce positive pressure at said bore and, in reverse running conditionof said rotor, to produce negative pressure at said bore.